The distribution of MSP1 within late trophozoites and schizonts.

<p>Panels A–C show the appearance of the single food vacuole, prepared for EM morphology. Panel A shows a late trophozoite containing a typically dilated food vacuole, containing widely spaced hemozoin and several profiles of internal membranous structures. In panel B an early schizont stage vacuole contains some hemozoin crystals and internal membrane profiles, while the vacuole wall shows signs of inward folding (arrowheads). C shows another schizont where a lipid body has formed adjacent to the food vacuole. Panels D–G show specific immunogold labeling of early to mid-stage schizonts labeled with MSP1₁₉-specific antibodies, in all cases detecting the protein at the vacuole wall. In panel D a limited area of labeling is present along one side of the food vacuole (small arrows), and in E a similar distribution is seen on a more folded vacuole wall. Panels F and G show labeling along obliquely sectioned folds of the wall (arrows), where the label also lies close to hemozoin crystals. Panels H and I show food vacuoles of late-stage schizonts containing closely packed large hemozoin crystals and are almost completely surrounded by MSP1₁₉ labeled vacuole wall membrane. In Panel J (and the inset of a portion at higher magnification) an early-/mid-stage schizont has been immunostained with antibody reacting with N-terminal regions of MSP1 but not MSP1₁₉. This antibody labels the newly synthesized (full-length) MSP1 on the parasite's plasma membrane but fails to label the food vacuole, indicating that the MSP1₁₉-specific labeling, seen in panels D–I, is specific for MSP1₁₉ carried in on the parasite surface at invasion rather than new MSP1 recently synthesized by the schizont. <i>Abbreviations</i>: FV–food vacuole; Hz–hemozoin; Int mem–internal membranous structures; RBC–red blood cell.